Zillow home values lag the real market.
When prices are dropping, Zillow Zestimates don't drop soon enough.
When prices are rising Zillow Zestimate don't rise soon enough.
Right now prices are rising in the good school districts of Silicon Valley, so Zillow Zestimates are too low. A Zestimate is just a prediction of the market value. However, the true market value is what a willing buyer willingly paid to a willing seller for the house.
For 10791 Brookwell Drive, Zillow shows a Zestimate of $875,000. However, on the open market, this house sold for $938,000. The actual sales price, and thus market value, was 7% above Zillow. Zillow is behind. Zillow underestimates the actual market value by 7% in this Castlewood neighborhood right now.
Assuming Zillow's formula is offset approximately the same percentage in the same neighborhood, a reasonable guess is that 6397 Myrtlewood Drive is worth approximately 7% above the Zillow Zestimate price. Since the Zestimate for 6397 Myrtlewood Drive is $912,200, if it's true market value is 7% higher, then 6397 Myrtlewood Drive is worth $977,878. The listing price of $970,000 is just 6% above the Zillow Zestimate, so is reasonable based on comparison to 10791 Brookwell Drive, which sold 7% above Zillow.
The spreadsheet showing both is in this Excel Workbook.